In an image captured on a photographic element such as film, halation is the unwanted exposure surrounding the image of a bright object cased by light reflected from the rear surface of the film support. It is known to reduce the halation effect with the use of an AHU provided in the film to absorb unwanted reflected light.
To meet the requirements of modern, high-speed coating facilities, the thickness of the AHU is increased to ensure good quality coating and to carry a dye to absorb all the reflected light. Single sided films manufactured for the Printed Circuit Board (PCB) market may contain such an AHU. Typically the AHU contains a solid particle dye and can also contain other photographic addenda such as a sequestrant to complex with iron and copper to reduce the risk of ‘spotting’, especially in aged film. A typical dry coverage for such an AHU is approximately 2 g/m2 of material, usually made up of a mixture of gelatin and latex copolymer. Use of an AHU as opposed to a so-called ‘pelloid’ layer, which is an antihalation layer provided on the opposite side of the base from that on which the emulsions are provided, allows a single sided film with improved dimensional stability as a result of a reduced humidity expansion coefficient (HEC) due to the option of coating lower overall material coverages than conventional two-sided products.
Despite the improved dimensional stability resulting from the reduced humidity expansion coefficient provided by single sided films with AHUs, the thickness of the AHU can lead to undesirable consequences such as humidity curl and a high cost of manufacture due to relatively large amounts of material being required.
U.S. Pat. No. 5,910,398 (Schmidt et al), discloses a method of manufacturing a photographic glass plate having an antihalation layer. U.S. Pat. No. 4,957,856 (Suematsu et al), discloses a silver halide photographic material having a light-sensitive silver halide emulsion layer and a subbing layer including a dye. U.S. Pat. No. 5015562 (Toya et al) discloses a light sensitive material comprising a support having thereon at least one light-sensitive silver halide emulsion layer. At least one layer including a mordant or a dye is also provided.
A problem with photographic films for use in graphic arts and in the manufacture of PCBs is that regardless of whether a pelloid layer or an antihalation underlayer is utilised, or both, there remains a degree of dimensional instability with temperature and/or humidity, which is particularly problematic if a multi-layer assembly is intended to result, for example in the manufacture of PCBs, where misalignment can occur.
Typically, customers are advised to store and, preferably use, the films in ambient conditions, such as at 50% RH and 21° C.